255 AN ADVENTAGEOUS ASYMMETRY IN THE BURSTING PRESSORE OF FETAL MEMBRANES

Abstract

The association between prematurity and early rupture of amniotie membranes prompted studies of the tensile strength and elastic limit of human fetal membranes. Chorio-amniotic membranes were obtained from 14 uncomplicated, term pregnancies at the time of elective, repeat C-section. None of the mothers had been in labor, all of them had intact membranes prior to the section, and all of the infants were normal. Multiple sites were sampled from each amniotie sac by mounting samples between two circular surfaces (O.D. 3 cm) with a central tapered round hole (diameter 0.45 cm). Progressive increases in the pressure provided by a tank of compressed nitrogen were plotted by a X-Y plotter against the displacement of a rod by the stretched membrane up to the point of bursting.Human membranes had marked (>3 fold) variability in bursting pressure and elastic limit as compared to synthetic membranes of silicone or polyethylene polymer. There was a positive correlation between the pressure and the elastic limit at the point of bursting for samples of amnion (r=.53, p<10−6), chorion (r=.53, p<10−6) and the intact bilayer of the two membranes together (r=.27, p<10−6) but not for the synthetic membranes. The combination of amnion and chorion was about 7% stronger (p <.003) when pressure was applied from the fetal side as opposed to the maternal surface, although the bursting pressure of amnion or chorion alone was independent of the direction from which it was applied.